Boston bombing jury hears 'officer down' police radio call

BOSTON, March 11 (Reuters) - A Massachusetts Institute of
Technology police officer who found a colleague in his squad car
covered in blood three nights after the Boston Marathon bombing
frantically repeated two words into his radio "officer down,
officer down."

A recording of that radio call was played to jurors hearing
the trial of accused bomber Dzhokhar Tsarnaev, 21, on Wednesday,
as prosecutors turned to the charge that the defendant and his
older brother murdered MIT police officer Sean Collier on April
18, 2013, in an unsuccessful attempt to steal his gun.

Collier's death marked the start of a chaotic 24 hours that
saw the brothers carjack a man and hurl explosives at police
during a shootout that ended when Dzhokhar Tsarnaev roared off
in a car, running over and killing 26-year-old Tamerlan Tsarnaev
before disappearing into a drydocked boat in the Boston suburb
of Watertown. Police found him the next evening, after a
day-long lockdown of much of the Boston area when hundreds of
thousands of people hid in their homes.

The officer who found Collier, Sergeant Clarence Henniger,
said he was responding to a 911 call about possible shots fired
on MIT's Cambridge, Massachusetts, campus, just outside Boston.
Collier had visible bullet wounds to his temple, neck and hand
and was so covered in blood that Henniger struggled to pull him
from his vehicle.

"I could hear gargling coming from his mouth," Henniger
testified at U.S. District Court in Boston, where the jury
hearing Tsarnaev's trial will also decide whether to sentence
him to death if he is convicted of killing three people and
injuring 264 with a pair of homemade bombs at the April 15,
2013, race.

Jurors also saw surveillance footage of two figures
approaching Collier's police cruiser on the MIT campus, spending
about a minute at the car, and leaving. The only visible
suggestions of commotion in the video are the car's brake
lights, flashing on and off.

Collier's gun belt and holster were covered in blood,
evidence of Tsarnaev's clumsy but unsuccessful effort to steal
his handgun, prosecutors have said.

Tsarnaev's attorneys opened the trial by admitting he
committed the crimes of which he is accused, but are seeking to
spare him the death penalty by demonstrating he was following
the lead of his older brother.

Federal prosecutors contend Tsarnaev, who emigrated with his
family from Chechnya a decade before the attack, was driven by
an extremist view of Islam and a desire to take revenge on the
United States for military campaigns in Muslim-dominated
countries.

Prosecutor William Weinreb said in his opening statement
last week that it was unclear if Tsarnaev or his brother fired
the weapon that killed Collier but argued that both brothers
were equally culpable in the officer's death.

A graduate student at MIT, Nathan Harman, who was bicycling
on campus the night of the murder, testified on Wednesday that
he saw Tsarnaev leaning into the driver's side door of Collier's
car, but did not see the older sibling.

"I only saw the one person," said Harman.

MIT Police Chief John DiFava on Wednesday recalled chatting
with Collier about an hour before his death.

"I told him to be safe, and I left," DiFava said, adding it
was the last time he saw Collier, 27, alive.
(Editing by Scott Malone and Tom Brown)